Each year, literally millions of aluminum aircraft parts are anodized and painted in order to protect them against corrosion. Current industry practice in applying these finishes typically involves first placing a large number of parts on a rack, followed by anodizing all parts at the same time, and then unloading the rack and painting each part individually. Painting is generally accomplished via conventional spray painting techniques.
Because of the large numbers of parts involved, there are high labor costs associated with unracking. Eliminating or even reducing some of this labor can have significant cost benefits to the manufacturer. For this reason, there has been a long-felt need to develop better racks or racking systems that can permit parts to be both anodized and painted without unracking.
Most racking systems which are well-suited for anodizing or electroplating are not well-suited for painting, and vice versa. The reason for this is that each process has unique requirements that do not complement the other.
For example, anodizing and/or electroplating requires good electrical contact and continuity between the rack and parts. Generally, the rack must be capable of carrying large electrical currents This requires that the rack be made of an electrically-conductive material, and have large or heavy structure that is sufficient to carry the needed current loads Such requirements, however, are opposite to the requirements for a painting rack. There, the amount of structure should be minimized in order to reduce, as much as possible, shielding of the paint spray which causes shadowing.
In the past, it has not been economical to use common racks for both anodizing and painting in connection with large, elongated aircraft parts The structural make-up of the typical racking system was such that it shielded large areas of the parts from the paint spray. It was found that the large amount of labor associated with touching up shadowed areas increased overall production costs to such an extent that it was more expedient to unrack the parts after anodizing, and then paint them once-over by hand.
The following U.S. patents disclose racks which are suitable for anodizing or electroplating, but are unsuitable for painting: Leffel U.S. Pat. No. 1,010,648 issued on Dec. 5, 1911; Palmer U.S. Pat. No. 2,253,576 issued on Aug. 26, 1941; Midling U.S. Pat. No. 2,541,597 issued on Feb. 13, 1951; and Beebe U.S. Pat. No. 2,697,690 issued on Dec. 21, 1954. Although the racks disclosed in all of these patents generally meet the requirements for plating operations, none are suitable for painting because, as discussed above, they have too much shielding structure.
The patent literature does disclose certain kinds of racking systems that are suitable for both plating and painting operations. Notable examples of this re Kunkle U.S. Pat. No. 4,037,727 issued on July 26, 1977, and Dziedzic U.S. Pat. No. 4,679,526 issued on July 14, 1987. Similarly, co-pending U.S. patent application Ser. No. 07/269,580, filed on Nov. 10, 1988, and naming two inventors who are also named here, discloses a racking system that is effective for both anodizing and painting operations. However, all of these systems are usable in connection with plating and painting small parts, with some having greater utility than others. Unlike the present invention, none are particularly suitable for racking large parts.